scholarly journals Fjord network in Namibia: A snapshot into the dynamics of the late Paleozoic glaciation

Geology ◽  
2021 ◽  
Author(s):  
Pierre Dietrich ◽  
Neil P. Griffis ◽  
Daniel P. Le Heron ◽  
Isabel P. Montañez ◽  
Christoph Kettler ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Ice Age ◽  
Late Paleozoic ◽  
Isostatic Adjustment ◽  
Climate Regulation ◽  
Continental Shelves ◽  
Glacial Dynamics ◽  
Ice Sheet Dynamics ◽  
Sedimentary Fill ◽  
Glacial Morphology

Fjords are glacially carved estuaries that profoundly influence ice-sheet stability by draining and ablating ice. Although abundant on modern high-latitude continental shelves, fjord-network morphologies have never been identified in Earth’s pre-Cenozoic glacial epochs, hindering our ability to constrain ancient ice-sheet dynamics. We show that U-shaped valleys in northwestern Namibia cut during the late Paleozoic ice age (LPIA, ca. 300 Ma), Earth’s penultimate icehouse, represent intact fjord-network morphologies. This preserved glacial morphology and its sedimentary fill permit a reconstruction of paleo-ice thicknesses, glacial dynamics, and resulting glacio-isostatic adjustment. Glaciation in this region was initially characterized by an acme phase, which saw an extensive ice sheet (1.7 km thick) covering the region, followed by a waning phase characterized by 100-m-thick, topographically constrained outlet glaciers that shrank, leading to glacial demise. Our findings demonstrate that both a large ice sheet and highland glaciers existed over northwestern Namibia at different times during the LPIA. The fjords likely played a pivotal role in glacier dynamics and climate regulation, serving as hotspots for organic carbon sequestration. Aside from the present-day arid climate, northwestern Namibia exhibits a geomorphology virtually unchanged since the LPIA, permitting unique insight into this icehouse.

scholarly journals Antarctic Palaeotopography

2021 ◽  
pp. M56-2020-7
Author(s):  
Guy J. G. Paxman
Keyword(s):  
Ice Sheet ◽  
Future Research ◽  
Dynamic Topography ◽  
Antarctic Ice Sheet ◽  
Isostatic Adjustment ◽  
Subglacial Topography ◽  
Mantle Processes ◽  
Ice Sheet Dynamics ◽  
The Antarctic

AbstractThe development of a robust understanding of the response of the Antarctic Ice Sheet to present and projected future climatic change is a matter of key global societal importance. Numerical ice sheet models that simulate future ice sheet behaviour are typically evaluated with recourse to how well they reproduce past ice sheet behaviour, which is constrained by the geological record. However, subglacial topography, a key boundary condition in ice sheet models, has evolved significantly throughout Antarctica's glacial history. Since mantle processes play a fundamental role in the generation and modification of topography over geological timescales, an understanding of the interactions between the Antarctic mantle and palaeotopography is crucial for developing more accurate simulations of past ice sheet dynamics. This chapter provides a review of the influence of the Antarctic mantle on the long-term evolution of the subglacial landscape, through processes including structural inheritance, flexural isostatic adjustment, lithospheric cooling and thermal subsidence, volcanism and dynamic topography. The uncertainties associated with reconstructing these processes through time are discussed, as are important directions for future research and the implications of the evolving subglacial topography for the response of the Antarctic Ice Sheet to climatic and oceanographic change.

scholarly journals ESD Ideas: Propagation of high-frequency forcing to ice age dynamics

2019 ◽  
Vol 10 (2) ◽  
pp. 257-260 ◽  
Author(s):  
Mikhail Y. Verbitsky ◽  
Michel Crucifix ◽  
Dmitry M. Volobuev
Keyword(s):  
Conservation Laws ◽  
High Frequency ◽  
Ice Sheet ◽  
Ice Age ◽  
Ice Flow ◽  
Age Dynamics ◽  
Nonlinear Character ◽  
Continuous Background ◽  
Ice Sheet Dynamics ◽  
Flow Conservation

Abstract. Palaeoclimate records display a continuous background of variability connecting centennial to 100 kyr periods. Hence, the dynamics at the centennial, millennial, and astronomical timescales should not be treated separately. Here, we show that the nonlinear character of ice sheet dynamics, which was derived naturally from the ice-flow conservation laws, provides the scaling constraints to explain the structure of the observed spectrum of variability.

scholarly journals ESD Ideas: Propagation of high-frequency forcing to ice age dynamics

2018 ◽  
Author(s):  
Mikhail Y. Verbitsky ◽  
Michel Crucifix ◽  
Dmitry M. Volobuev
Keyword(s):  
Conservation Laws ◽  
Time Scales ◽  
High Frequency ◽  
Ice Sheet ◽  
Ice Age ◽  
Age Dynamics ◽  
Linear Character ◽  
Astronomical Time ◽  
Continuous Background ◽  
Ice Sheet Dynamics

Abstract. The observational records display a continuous background of variability connecting centennial to 100-ka periods. Hence, the dynamics at the centennial, millennial, and astronomical time scales should not be treated apart. Here, we show that the non-linear character of ice sheet dynamics, which was derived naturally from the conservation laws, provides the scaling constraints to explain the structure of the observed spectrum of variability.

Glaciomarine environments in Canada: an overview

1993 ◽  
Vol 30 (2) ◽  
pp. 354-371 ◽  
Author(s):  
James P. M. Syvitski
Keyword(s):  
Ice Sheet ◽  
The Arctic ◽  
Accumulation Rates ◽  
Ice Shelves ◽  
Sediment Yields ◽  
Continental Shelves ◽  
Iceberg Calving ◽  
Ice Sheet Dynamics ◽  
Glaciomarine Sediments ◽  
Ice Complex

The present understanding of Canada's glaciomarine environments owes much to the remarkable role played by the scientists of the Geological Survey of Canada. Their efforts have led to the review and partial revision of three scientific paradigms: (1) There is a mechanical rather than a climatic control of the collapse of a tidewater ice sheet; (2) ice sheets were mostly grounded on Canada's continental shelves (rather than with floating ice shelves); (3) ice-loaded glaciomarine sediments are sometimes indistinguishable from deposits of till. A proposed stratigraphic framework for Canadian glaciogenic sequences can be quantified, allowing insights into ice sheet dynamics. For instance, the arctic margin of the Wisconsinan ice complex appears to have generated comparatively little meltwater, ice margin retreat being principally by iceberg calving. Surprisingly, the Atlantic margin of the Wisconsinan ice complex appears to have transported larger quantities than its Pacific counterpart. This is contrary to the present postglacial sediment yields discharged onto each margin. Glaciogenic sedimentation rates are shown to vary with the distance from a sediment source and the delivery rate of sediment. Glaciogenic accumulation rates are dependent on basin history and basin shape. Numerical examples include (1) the determination of accumulation rates from carbon stratigraphy; (2) the evaluation of the flux of sediment from a fjord to the open shelf during the retreat phase of an ice sheet; and (3) the application of a basin fill model to predict the styles of sedimentation within a fjord.

scholarly journals An ice-sampling programme in the Thule area, North Greenland

1987 ◽  
Vol 135 ◽  
pp. 81-84
Author(s):  
N Reeh ◽  
H.H Thomsen
Keyword(s):  
Great Britain ◽  
Ice Sheet ◽  
Ice Age ◽  
Geological Museum ◽  
Climatic History ◽  
Last Ice Age ◽  
Sampling Programme ◽  
Ice Sheet Dynamics ◽  
Area North ◽  
North Greenland

A glaciological programme was carried out as part of the NORDQUA 86 expedition to the Thule area, Nbrth Greenland, from 7 to 24 August 1986. The expedition included researchers from the five Nordic countries and Great Britain and was organised by the Geological Museum, Copenhagen (Funder, in press). The expedition had a Quaternary geological programme, as well as a glaciological programme dealing with the climatic history and ice-sheet dynamics before and during the last Ice Age in the area.

Leveraging non-traditional evidence for glacial isostatic adjustment to constrain past ice sheets

2021 ◽  
Author(s):  
Tamara Pico
Keyword(s):  
Sea Level ◽  
Current Knowledge ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Age ◽  
Small Scale ◽  
Glacial Isostatic Adjustment ◽  
Continental Scale ◽  
Isostatic Adjustment ◽  
Ice Stream

<p>Although understanding the response of ice sheets to a changing climate is a pressing issue of this century, our current knowledge of past ice-sheet changes remains limited by data sparsity. I explore approaches that leverage non-traditional datasets to constrain past ice sheet and sea-level change over the last glacial cycle. For example, I consider the potential to use past landscapes to infer crustal deformation induced by ice sheet loading. Over the ice-age, glacial isostatic adjustment produces rates of uplift comparable to some of the fastest tectonic uplift rates (~10 mm/yr) in regions hundreds of kilometers away from the maximum ice sheet extent. Additionally, I show it is possible to gain insight into longer-term continental scale ice sheet deglacial histories using small-scale ice stream dynamics. Using records for a rapid retreat of the Amundsen Gulf Ice Stream, located on the northwest Laurentide Ice Sheet, along with observations of the Bering Strait flooding as sea-level indicators, I fingerprint the timing and location of North American saddle deglaciation.</p>

scholarly journals Causes of ice age intensification across the Mid-Pleistocene Transition

2017 ◽  
Vol 114 (50) ◽  
pp. 13114-13119 ◽  
Author(s):  
Thomas B. Chalk ◽  
Mathis P. Hain ◽  
Gavin L. Foster ◽  
Eelco J. Rohling ◽  
Philip F. Sexton ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Phase Locking ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Age ◽  
Climate Forcing ◽  
Testing Hypotheses ◽  
Ice Sheet Dynamics ◽  
The Relationship

During the Mid-Pleistocene Transition (MPT; 1,200–800 kya), Earth’s orbitally paced ice age cycles intensified, lengthened from ∼40,000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets.

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